Alkaline batteries have become increasingly more popular because of their high energy density. As such, these batteries are increasingly used in applications normally reserved for the traditional lead-acid battery systems.
In order to achieve extended battery life and efficiency in alkaline systems, the use of battery separators is required and the use of battery interseparators, as well, is preferred. The battery separators are located between the positive and negative plates so as to provide, (1) a separation between the electrodes of opposite charge, (2) an electrolyte reservoir, (3) a uniform electrolyte distribution across the electrode surface so as to permit uniform current density and (4) a space for electrode expansion.
Battery separators and interseparators used in alkaline batteries at present are commonly formed of polypropylene, polyamide and/or nylon non-woven sheets.
Other separators in use in alkaline systems today are shown in U.S. Pat. Nos. 4,264,691 and 4,330,602. The separator/interseparator is formed of synthetic pulp, alkali resistant inorganic filler and a long fiber of polyester, polyacrylic, polyamide or polyolefin materials.
Until now, these separators have been suitable for nickel cadmium ("Nicad") batteries. However, a newer battery design is poised to supplant the Nicad battery as the rechargeable alkaline battery of choice. It is known as the nickel/metal hydride battery.
The nickel/metal hydride battery offers the potential of higher energy densities, longer life and the elimination of the use of cadmium, which is costly and has questionable environmental acceptability.
The nickel/metal hydride system requires a separator with better performance characteristics than is currently available with the current separators, especially those based upon nylon.
The present invention overcomes the problems inherent in the currently used separators and provides an inexpensive sheet material with the desired tensile strength, chemical inertness, thickness and wicking properties and which is particularly usable in nickel/metal hydride batteries.